Compare the Breathing Rates of a Goldfish and a Human (page 2)

Design Your Own Experiment

1. How does temperature affect the breathing rate of fish? Use a fishnet to carefully transfer fish 1 to the test jar. Place a thermometer inside the jar. Set the jar in a bowl half filled with water. Lower the temperature of the water inside the jar by two-to-five degree intervals by adding small pieces of ice to the water in the bowl (see Figure 21.2). Gently stir the water in the jar with each addition of ice to reach a uniform temperature and record that temperature. At each temperature interval, it is important to wait five minutes to allow the fish to adjust to the new temperature. Too sudden a temperature change could injure the fish. Count the number of times the fish opens and closes its mouth in two minutes and divide by 2 for the breathing rate per minute. Continue lowering the temperature until 41 ° F (5 ° C) is reached. Do not be concerned if exact temperature increments are reached. Allow the jar to sit and warm before returning the fish to the aquarium. Repeat the experiment for each fish. Construct and display a graph showing the average breathing rate of each fish at each of the different temperatures (see Figure 21.3).
2. Does increased activity affect the breathing rate of fish? Place fish 1 in the test jar. Maintain a constant water temperature. Cover the jar with a dark cloth and do not disturb the fish with noise or movement for five minutes. Position yourself so that you can immediately begin counting mouth movements as you quickly remove the cloth. Determine the startled fish's respiration rate. Repeat the procedure for each fish.
3.  
   1. How does the breathing rate of fish compare to that of air breathers such as humans? Choose a test subject. Count the number of times the person breathes during two minutes. Repeat the counting process twice. Average the three trials and divide by 2 to calculate the breathing rate of the person for one minute. Make an effort not to inform the person that you are observing his or her breathing.
   2. Does the breathing rate change if the person is aware of being observed? Repeat the experiment explaining to the test subject what you are doing.
   3. How does exercise affect the breathing rate of air breathers? Repeat the experiment twice, first measuring the breathing rate of the test subject at rest, and then measuring the rate after the subject has quickly marched in place for two minutes. Be sure that this exercise does not endanger the health of the test subject.
   4. Use a photograph of your human test subject and a photograph of one of the test fish to represent the breathing rates of air and water breathers. Display information about the breathing rates and diagrams of air breathers that are more comparable in size to the fish.

Get the Facts

1. The breathing of a fish is like a two-way pump. Water is pulled into the mouth and pushed out the gills. Use a biology text or science encyclopedia to find out more about this mechanical process and how oxygen is extracted from the water. What is the purpose of gill filaments and gill rakers?
2. The requirement of oxygen for a fish changes with water temperature. As the temperature rises, the metabolism of the fish increases; thus, more oxygen is needed. At the same time, at a higher temperature water cannot hold as much dissolved oxygen; thus, the fish has to inhale more water to meet its oxygen demand. Use a biology text to find published values for oxygen content of water at different temperatures and the oxygen-consumption requirement of fish per weight unit. Use a pharmacy scale to determine the exact weight of your fish. Place one fish in a jar of water and weigh it. Weigh the jar with the exact amount of water without the fish. Calculate the weight of the fish. Do this for each fish and use the weights to determine the ventilation rate (amount of water inhaled per weight unit per hour) of each fish.

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